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IIRC there was a TSB on this and the problem was with 05-08 model years. I believe the gasket material/design was changed and the problem was solved. [/quote]
I have read that Toyota did change the part number for the 1GR-FE head gasket sometime around 2007 or 2008, and so they probably recognized a problem and made changes. Hopefully, the problem is solved for vehicles newer than my 2006. People who have approached Toyota to cover the 4.0L head gasket failures out of warranty have basically been told to go pound sand - so far.
I have a hypothesis about what might be a contributing factor, and I don't know whether the 5th Generation 4Runners are designed the same as the 4th Generation. From what I have read, most, if not all, failures have begun with leaking into an even-numbered cylinder, which are located on the driver's side of the motor. If you follow the exhaust from the manifold on the paseenger's side, it goes nearly stratight back all the way to the tailpipe. However, the driver's side exhaust comes off the manifold and makes a near 90 degree turn under the transfer case and connects with the passenger side pipe. In addition, where the exhaust pipe goes under the transfer case, it is flattened and constricted so as not to protrude any lower than the frame crossmember in that area.
I imagine that the gasket used on the left and right cylinder banks is the same. Because the failure appears to always happen on only one side, there must be something causing it other than random gasket failure. I'm thinking that there might be more heat build-up in the even-numbered cylinders because of the convoluted exhaust routing and constriction. If there is anything to this hypothesis, hopefully the new gasket material will be up to the job.
I would be curious to know whether anyone with a 5th Generation 4Runner has ever noticed how the exhaust flows back to the tailpipe, especially on the driver's side.
